The present invention relates to a seat structure for a vehicle, and particularly to a seat structure for a vehicle which comprises a seat cushion, a seatback, and a headrest.
It is required for a seat of a vehicle to ensure the safety of a passenger in a rear-end collision of the vehicle, in addition to the performance of the seat itself, such as the function of holding a passenger's position and the comfortableness. The rear-end collision of the vehicle occurs when the vehicle is hit from behind by another vehicle or the vehicle moving backward hits against an obstacle or something. In the rear-end collision of the vehicle, a load acts on the seat from the rear, so that a passenger is pressed against a seatback and a headrest. In this case, it is necessary to control such that the position of a passenger's head portion does not improperly change relative to the headrest in order to prevent whipping of the passenger properly.
More specifically, in the vehicle rear-end collision, a rearward load operative to cause a rearward move of the seat relative to a vehicle body due to the force of inertia acts on the seatback mainly. Consequently, another load operative to push down a rear portion of the seat cushion in which the passenger is seated occurs, too. When the rear portion of the seat cushion lowers, there is a concern that the position, in a vertical direction, of the head portion of the passenger relative to the headrest may change improperly.
In general, the seat cushion of the seat includes a frame member, such as a seat cushion frame, and this frame member is connected to and supported at a pair of slide mechanisms (a guide rail and a slider, primarily) which are provided at right and left both-side portions of the seat fixed onto a vehicle floor via a bracket for seat fixing or a lifter mechanism. That is, between the side mechanisms and the seat cushion are provided a pair of right-and-left connecting members which connect the side mechanisms and the seat cushion and support the seat.
Japanese Patent Laid-Open Publication No. 2012-148721, which shows the above-described fixation structure (support structure), discloses a seat structure in which a lifter mechanism is provided between a floor of a vehicle body and a seat cushion. According to the seat structure disclosed in the above-described patent document, the distance, in a vertical direction, between the floor and the seat cushion is so long because of providing the lifter mechanism that the amount of lowering of the rear end of the seat cushion tends to increase. Therefore, the seat structure of the patent document is configured such that a rear link of the lifter mechanism comes to contact a stopper in the rear-end collision, thereby restraining the amount of lowering of the rear end of the seat cushion.
Herein, the inventors of the present invention and others have considered a seat structure in which at both sides or one side of the pair of right-and-left connecting members, a connection position of the lifter mechanism and the seat cushion frame is located inward in a seat width direction relative to a connection position of the lifter mechanism and the slide mechanism in order to provide a properly small-sized lift mechanism for the light-weight achievement. However, in this seat structure, when the rear-end collision of the vehicle occurs, the lift mechanism tends to fall down toward the inside of a pair of slide rails (i.e., move inward in a seat width direction) due to the above-described load acting on the seat. Herein, there is problem in that in a case in which the above-described situation happens, the rear link and the stopper of the above-described patent document may not properly restrain the rear end portion of the seat from lowering.
Herein, in a case in which at both sides of a pair of right-and-left lift mechanisms, the connection positions of the lifter mechanisms and the seat cushion frame are located inward in the seat width direction relative to the connection positions of the lifter mechanisms and the slide mechanism, the passenger also lowers as an entire part of the rear portion of the seat cushion lowers, so that there is a problem in that the position of the passenger's head may change vertically relative to the headrest. Meanwhile, in a case in which at one side of the pair of right-and-left lift mechanisms, the connection position of the lifter mechanism and the seat cushion frame is located inward in the seat width direction relative to the connection position of the lifter mechanism and the slide mechanism, the passenger also slants as only the one side of the rear portion of the seat cushion lowers mainly, so that there is another problem in that the position of the passenger's head may change vertically and laterally relative to the headrest.
Further, the above-described problems happen not only to the seat equipped with the above-described lift mechanism(s) but also to a seat structure designed for different types of vehicle for commonality in which the width of a seat itself is set to be relatively short for a particular type of vehicle and a connection position of a bracket for seat fixation and a seat cushion frame is located inward in the seat width direction relative to a connection position of the bracket for seat fixation and a slide mechanism.